The present invention relates to flexible electrical cables having braided wire shields surrounding an inner conductor assembly, and particularly to improvements to such cables which provide exceptional pliability and limpness for minimizing the resistance to movement imposed by such cables on devices to which they are attached.
Multi-conductor electrical cables having an inner conductor assembly with a dielectric covering surrounded by a braided wire shield, as shown for example in U.S. Pat. No. 4,552,989, are now in common use for rapidly transmitting signals to and from sophisticated electronic equipment. Although such cables are flexible, such flexibility is insufficient for certain applications. For example, when such cables are attached to hand-held devices such as medical diagnostic instruments, where maximum maneuverability of the devices is required, the limited flexibility of such cables can cause excessive resistance to movement of such devices in all directions, as well as excessive resistance to axial twisting of such devices.
Some cable designs, such as that shown in U.S. Pat. No. 3,665,096, have been developed to improve the flexibility of cables by eliminating the braided wire shield and substituting therefor more complex types of shields with lesser stiffness than a braided shield. However, such designs are not only substantially more expensive to manufacture, but fail to recognize that the stiffness of the shield itself is not the primary factor affecting cable flexibility.
Certain other types of electrical cables, such as those shown in U.S. Pat. Nos. 2,006,932, 2,234,675 and 2,866,843, provide spaces or clearances between various layered components of the cable to accommodate fluids for various purposes, but such spaces are not used in conjunction with braided wire shields nor are they effective to improve cable flexibility.
Coaxial cable transducers, as depicted in U.S. Pat. Nos. 3,763,482 and 3,921,125, have braided wire outer conductors snugly applied to the dielectric covering of an inner conductor with a capacitive gap (i.e. an effective electrical gap) between the outer conductor and the dielectric covering to provide a pressure-sensitive transducer action. However the snug application of the braided wire outer conductor prevents the braided wire and the dielectric material from moving freely in a longitudinal or rotational direction relative to each other, and thereby prevents the cable from attaining the high degree of flexibility or limpness needed for the special applications described above.